Nontumbling gyroscopic directional indicator



Oct- 30, 1951 J. s. ADKlNs ETAL NONTUMBLING GYROSCOPIC DIRECTIONALINDICATOR 2 SHEETS-SHEET l Filed March 8, 1948 Oct- 30, l951 J. s.ADKlNs ErAL NONTUMBLING GYROSCOFIC DIRECTIONAL INDICATOR 2 vSHEETS-SHEET2 Filed March 8, 1948 INVENTORS. 5. /Qae//VJ BY Jal/NJ ,e7-

YPatented Oct. 30, 1951 NONTUMBLING GYROSCOPIC DIRECTIONAL INDICATOR YJohn S. Adkins, Dayton, and John J. Hart,

Osborn, Ohio Application March 8, 1948, Serial No. 13,*734

(Granted under the act f March 3, 1883, as amended April 30, 1928; 3700. `Gr. 757) 3 Claims.

The invention described herein may be manufactured and used by or forthe United States Government for governmental purposes without paymentto us of any royalty thereon.

The present invention relates to a nontumbling gyroscopic directionalindicator including a settable reference dial.

The primary object of the present invention is to provide a gyroscopicdirectional indicator especially suited for use on pursuit aircraft oron any aircraft which are highly maneuverable. Because of the maneuversexecuted by such aircraft, the directional gyroscope is often subject tohaphazard gyrations, so that upon completion of the maneuvers theheading indicated may be seriously in error. Thus it is an importantobject of the invention to so arrange the gyroscope gimbal ring and stopmeans therefor that unusual maneuvers will produce a definite andlimited tumbling action of the gyroscope and so result in a minimum ofdeviation of the indicator.

Another object of the -invention is to provide a directional gyroscopefor aircraft including an indicating pointer for showing the instantaircraft heading in conjunction with a settable reference dial. Thepointer and dial arrangement makes possible a directional indicatorwherein the desired heading may be indicated when the p-ointer is insome arbitrary position, such as pointing vertically upward. This isdesirable in standardizing an instrument since this arbitrary straightup pointer position is now an accepted condition in all types ofaircraft instruments. Such a position of all the pointers of aninstrument board is intended to show that the aircraft is operatingsatisfactorily.

A further object of the invention is to provide an improved cagingmechanism for a gyroscopic indicator.

A further object of the invention is to improve the structuralarrangement of elements in and extend the field of usefulness ofgyroscopic directional indicators. A related object is to provide agyroscopic directional indicator having reliable and predictableoperating characteristics. The above and other objects of the inventionwill become apparent upon reading the following detailed description inconjunction with the' drawings, in which:

Fig. 1 is a vertical cross sectional view of the gyroscopic directionalindicator, showing the essential elements contained within the outershell or casing.

Fig. 2 is a front elevation view of the dial and pointer as used on thepresent directional indicator.

Fig. 3 is a detail view, partly in vertical cross section, the cagingmechanism of the gyroscope.

Fig. 3a is a detail View Qi a PQitiQ!! Qi the lnot illustrated in thepresent drawings.

mechanism shown'in Fig. 3, but illustrating a modification of the cagingmechanism.

Fig. 4 is a vertical cross sectional view taken on the line 4 4 of Fig.1 to shown the angular range of movement of the gyroscope rotor andenclosing case therefor within the mounting ring or gimbal ring.

The presently disclosed gyroscopic directional indicator or directionalgyroscope is of the electrically operated type, similar in this andother respects to the'directional gyroscope described and illustrated inU. S. Letters Patent No. 2,406,341 granted to Lennox F. Beach et al. onAugust 27, 1946. The detailed arrangements for making electricalconnections to the vertical mounting ring Aand to the rotor assemblybeing shown in the patent, these specific details are In any case it iswell understood that electrical connections to rotating elements mustVbe made through suitable slip rings or insulated pivots engaged b`relatively stationary spring brushes.

BASIC GYROSCOPE ASSEMBLY For a description ofthe present indicatorreference is made to Fig. 1, wherein the complete device is shown exceptfor portions Vof the gyro caging mechanism. The indicator includes acasing or housing I and attached frame assembly 2, both of box-likeshape.' At the front end of the frame assembly there are the dialsupporting 'member 3, and the crystal supporting member 4.

At the rear end of the framer assembly there are a pair of plate-likemembers 5 and 5' and to the latter members there is secured the casing Iby means of screws 6. The front end of the-casing is in abutment withgasket material forming part of the crystal supporting member 4. Securedto the back plates 5 and 5' there is a special electrical outlet 1,which includes prongs to supply all the needed electrical energy foroperation of the gyro rotor and electromagnetic gyro erecting means. Thepreferred source of power on aircraft is the usual volt, 400 cyclerthreephase inverter, the outlet 'l thus requiring three prongs.

The frame assembly 2 includes a top bearing plate 8 and a bottom bearingplate 9 secured in any suitable manner, as by means of screws Yforinstance. Antifriction bearings 8' and 9' centrally located on theseplates provide means'to rotatably mount the gimbal ring I0`on an axis:1J-y which is normally vertical, that`is with the aircraft in levelflight position. The opposite vertical side portions of the ring l0 areprovided with antifriction bearings to mount trunnions I I and I2 of thegyro assembly G. The gyroA assembly G is thus mounted for free rotationon the normally horizontal axis :c-z. The g'yro assemblyGscoinprisesfacylindrical casefor .housing I 3 ywithinewhic'h.is...rotatably;mountedia .gyro rotor I4, the normally horizontal axis ofwhich is indicated at e-a. The gyro assembly G forms ,-a small inductionmotor, the case I3 being the stator, and the rotor I4 enclosedthereinhaving y sufficient mass to give the desired gyroscopic stability athigh rotative speeds. Suchzafltotor tends to maintain itself in spacewith the axisiin the same relative position at .all times,. thischaracteristic of gyro-stability andthe 'furthercharacteristic calledprecession being the .principal operating features of all gyroscopes.iFixed .on the left hand end of the case fthere isgasectorlike cagingbar I5, the -,profile of which is well illustrated in Fig. 4. Fixed onthe right hand end-of the case I3 `there -is a leveling switch memberAI6 resembling fa twoesecton commutalftoryorilyfonemf `whichsectionsfmaybe seen in "l, t1Ihe 'circuits through the 'switch :are 20clesedby fmeans vv(f fspring arm'brushes |21 and 'thusf-being'open.The-opposite lend portions I5 and I'5 o`f the fbar I5 are vadapted tocontact a stop-member 'I9'secured to the gimbal'ring `If0 coincidentw'ithfthe central iplane'thereo'f. The range `fof :movementrallowed -:bythe-barfand bar stop may vary from about 82 to 89 degrees either wayfromthenormal position o'f -Fig. 1 ,"butfthe fpreferredfamount of angularmovement is :86 de- ?grees. This-angle vof rotation ofthe gyro assem-'blyGwill be referred toin more detail below but it {is V'noted thatFig. v'illustrates vthe normal `-rspaced relation of the -bar and 'barstop. "The `-:angles -of rotation ofthe gyro-assembly in'feitherdirection are -designatediby the arcs A Aand A" 4in Fig.=4. VAThebar f5is valso'notched'at I 5a "to vreceive the freefend 'cfa 4pivoted pagingarm to be described below.

'The-verticalgim'bal ring I0 rotatably mounted "to .turn aboutthe axisy-y has rigidly mounted thereon at theupper side a vtorque rotor '20 in-'fcluding rotor windings 2l. Mounted on the "frame assembly '2 withinthe confines of thebearingiplate-S is a squirrel cage l"212.,which'reacts Aelectrcrnagnetically withthe rotor `v2l) to provide Iatorque vraction on the gimbal ring I0. This torque Jproduces aprecessingl'couple adapted to influence-the relative position-of the gyro assemblyG about the :iz-a: axis, since the couple is ap- :plie'd vtothe gimbalring of 4the `gyroscope in a V:plane 'lying at arig'ht angle to theplane of lrotationV o`f gyro assembly-G. 'The theory of pre- -cession isdescribed in `somefdetail in The Theory :sof nthe Gyroscopic fCompass byA. L. Rawlings *"(second 'edition-#1944). "Power connections yarefmade'to the ft'orquer2`f2 I ,122 'through the leveling fswitch I6, ITI,I8. The torquerhaving-awindin-g 221| vcapable of reversing the/directionlof torque byproper connections thereto, the'switc-h I6, I 1, t8 isithusfadapted to reversethe torquing :action mi':thetorquereas'rthegyroassembly G tilts to one .side or fthe Vother fromthe-normal postioniigs.

'4 f1 andai) Theitorque v121|, f2 I ,22 fis .merely an induction motorand if ...there .is a circuit thereto completed through the levelingswitch when the gyro rotor i4 is not spinning, the torque will operateto spin the gimbal ring I0 about the axis gy-T111. However with theinstrument in use the gyro rotor I4 is spinning rapidly and its gyro-.zscqpic-sstabilityreffectively resists displacement of :the gyroassembly G and also the gimbal ring I0 from the normal position.Application of power to the /torquerthus acts merely to precess the.assembly G back to its normal position in which no current passesthrough the leveling switch or .the targuer.

CAGING MECHANISM tThe :gyro-assembly G is^cagedor'1ocl ed in the rnormalposition (Figs. V1 and 4) whenithe caging mechanism is actuated. 'Thismechanism will now be described starting with 'the caging knobmv3Il'`(Fig. 13). 'Fixed to theknob lby a set screw there'eisa cagingshaft 3| slidably and rotatably mounted in the crystal supporting memberor 'ffacefplatel The'inner end 4ofthe shaft 3I con- "tactsa'cagingslidef32 movablymounted on the 'baseo'fifr'ame assembly 2. A detentmember 133 npivotally mounted on the frame assembly at "34 vis-spring-urged upwardly V'by meansfof a coil wspring 35 connected to thedetentlb'elow the'pivot point :34. `The opposite end of the Spring fssls`-s'ecured to caging slide 32f which is `thus urged 'toward the shaft 3Iat all times. VThe end of slide 32 'adjacent to the detent33 has aturnedhin contact'face portion which'in the uncaged positionretains the detentin the'lower dotted'line y'position. 'When the slide V32 reaches theinner positionlasvshown under pressure exerted through shaft 23|,thedetent Y33 snaps up to the full line 'positiontoprevent return of theslide 32. At the same tme'further upward `movement 0f the de- V'tent-ispreventedby contact of `the yprojection'iii 'with -a reduced portion3Ivof shaft 3l. To re- "-lease^the detent and caging slide the shaft 3|is pulledfoutwardly to cam thejdetent downwardly, thus nreleasing thecaging slide 32 for forward movement Rotatably mounted on the base offrame aslsembly 2 Ythere is a cam ring 36 (see Fig. 1), "whichisiturnedfabout its center by the casing ,5D-slide 32. The connectionbetween the slide and .55 slide and ring respectively. The cam ring 36is '-'urged'to the uncaged position by a coil spring 38, connected ltolugs on the frame assembly and ring. 'The ring `36 has formed in itsedge flange three-orV more cam slots 39 to receive a similar number ofcam pins 40 secured in an annulus FLI. The 'inner ends of the pins 40extend into lvertical vslots 3'9 in the 'bearing plate 9, so that"the'annulus 4I must rise as the cam ring 36 is Airotated. Thisconstruction may also be seen in the patent to Beach et al. previouslyidentified '1(see1Figs. '1, 2 and`3 of the patent). As the an- `nulu's45| rises pressure lis exerted on a push rod SA'Z'Yhaving its upper endin engagement with a caging arm 43 pivotally mounted at 44 and spring'urged downwardly. 'The-'free end 43 of the varm is adapted to/contact'the-fcaging bar I5 and rock the bar and gyro assembly into thenormal'posi- 'tion whereupon the arm engages the notch I5a of `:bar '115ito retain the-'gyro'assembly G in the 'normalscaged position,fasin'fFigs. l and 4. As

lthe ring 41.

may be seen in Fig. 4 the caging bar I5 has a circular outline with thecenter of curvature thereof being spaced above the axis of rotation ofthe rotor case so that pressure exerted by the caging .arm will alwaysrotate the bar and rotor case to the normal caged position. The cagingelements such as the slide 32, ring 36, annulus 4|, push rod 42 and arm43 are all retained in the caged position by virtue of the detent 33,and if the detent is released by return movement of shaft 3| all theforegoing elements return to their uncaged position by virtue of springsacting individually thereon. The spring for arm 43 is a small leafspring 45 bearing on the arm near the pivot 44, the downward return ofthe arm being adapted to return the push rod 42 to the lower position ofFig. 1. As the annulus 4| rises it is also adapted to engage the underface portions of pins 46 slidably mounted in a ring 41 carried on thelower side of gimbal ring I0. These pins 46 are urged downwardly by leafsprings 48 secured on With the annulus 4| in the raised position, thecontacting relation of the annulus 4| and the pins 46 causes frictionallocking of the gyroscope gimbal ring I6 with respect to its normalrotation about the axis y-y. The operation of caging the gyroscope asjust described is done to temporarily stabilize the instrument and topositively set the gyro assembly G in the normal position, wherein theaxis y-y is at a right angle to the axis z-e.

The ring 41 also serves another purpose besides that of carrying thefriction pins 46. Mounted on the plate 5 adjacent to the ring 41 thereis a small solenoid 50 having a springprojected armature 5|. Thearmature is adapted to contact the outer edge of ring 41 when thecircuit to the solenoid is broken, thus frictionally locking the gimbalring I against free rotation about the 'y-y axis. The solenoid 50 isconnected in series with the windings of gyro rotor I4, so that when thepower to the instrument is cut off the armature will instantly apply abraking force to the ring 41. Upon landing the aircraft the power supplyis usually turned oif, and power to the gyroscope is thus cut off. Asthe rotor |4 runs down it may cause tilting of the gyro assembly G androtation of the gimbal ring lll, if the automatic solenoid brake is notpresent. Therefore the solenoid as described forms a convenientstabilizing adjunct in the instrument. It might be noted further thatthe caging mechanism is never left .in set position when the aircraft ison the ground, since this would place strains on the bearings.particularly in taxiing the aircraft over the ground.

SETTABLE DIAL AND POINTER The instrument includes a dial supportingmember 3 as noted above. Extending centrally through the member 3 is adrive shaft 60 having rigidly secured thereto a large bevel gear 6|.Meshing with gear 6| is another bevel gear 62 fastened to the top of thegimbal ring IU coaxially with respect to the axis y-y (see Fig. 1). Thusthe rotation of gimbal ring |0 about the y-y axis results in rotation ofthe shaft 60. Pinned to the shaft 66 is a gear wheel 63, and securedcentrally to the gear wheel is a hub 64 carrying a pointer 65. Securedto the member 3. is circular plate 66 having a central hub portion 66',within which is rotatably mounted the pointer hub 64. The central hubportion 66 carries a flange and between this flange andthe plate 66there is mounted a circular dial or card 61 having peripheral gear teeththereon. The card 61 turns on the hub portion 66 but always remains inany selected position due to friction between the card and its centralmounting means.

. As shown in Fig.' 3 the shaft 3| extends rthrough a cup-like bushing68 threaded into the frame 2 and locked in position by means of a nut69. Seated in the bushing is the hub portion of a gear member 10,through which the shaftBl extends. The shaft 3| may slide in the bushingbut relative rotation therebetween is prevented by engagement of across-pin 1| on the shaft which rides in a slot formed in the hub ofgear 16. Limited relative sliding movement .is also possible but theshaft tends to take a definite position with respect to the gear hubdueto a coil spring 12 in the hub which is engaged by a cross-pin 13 onthe shaft 3|. Thus the spring forces the shaft outwardly until thecross-pin 1| engages the outward end of the slot associated therewith.Further outward movement of the shaft caused by a pull on knob 30carries the gear 16 outward into driving engagement with the gear teethof card 61. As shown in Fig. 3 the gear 19 is in driving engagement withgear 63, which is directly connected to the pointer 65. The driving gearor pinion 10 stays in this position while the gyroscope is caged, eventhough the shaft 3| does spring outward slightly after manual pressureis taken off the knob 30. The driving gear 10 is moved into engagementwith the peripheral teeth on card 61 at the same time the gyroscope isuncaged by an outward pull on knob 3U. Thus in the normal uncagedoperation of the instrument, the reference dial or card 61 may be setwith reference to the pointer. For instance, if a turn of a knownmagnitude is to be executed the card 61 may be rotated through a knownangle with respect to the pointer, and upon completion of the turn thepointer will read zero on the card thus informing the pilot that he hascompleted the turn. In the caged position of the gyroscope, the pointermay be set independently of the card so as to place the pointer in astraight up position opposite one of the xed reference marks R. Thenwhen the gyroscope is uncaged the on course position of the pointer willbe in the preferred straight up position, since the gyro assembly Gtends to hold to its original position because of the principle ofgyroscopic stability. As seen in Fig. 2 there are several referencemarks or indices R located around the dial in fixed relation to thecrystal supporting member 4. There are preferably two indices R. invertical alignment, and two more each at fortyve degrees from theuppermost index.

A modification of the dial and pointer drive means is shown in Fig. 3a.In this form of the gear drive, the card and pointer may be movedtogether when the gyroscope is caged but when it is uncaged only thecard 61 may be moved just as in the principal form of the invention(Fig. 3). As shown in Fig. 3a the slidable and rotatable shaft 3|,having a knob 30 secured thereto, extends through the crystal supportingmember 4 and also through the hollow bushing 68. Mounted on the shaft ina manner similar to the mounting of gear 10 in Fig. 3 there is a gear10a having teeth wide enough to drive both the card 61 and the gear 63at the same time. However when the shaft 3l is pulled outy toi theuncaged position, the

:amasar gear :flraiwill @mesh 'only A.with the .card '57, JOIaadiustmentithereof with respect ito the .pointer 65.

"GYROSCOPE FUNCTIONS .AND OPERTION The purpose of the present gyroscopicindi'- rcatoris to show the instant vheading of an air- `@ratti-havingthe indicator :mounted in 'front 'of Sthe pilot with the Idial in plainView facingft'o- "Wardthe rear of the aircraft. '.Wit'h the .fair--fcraft `on an 'even keel, the instrumentfca'se l y"willextend:horizontally and the y-'y :axis Vwill :extend in a Svertical direction.However 'the .axis extending through Vtrunn'ions lil fand S132 andthez-a axis V(known asthe spin axis il( "of the Aryg-yroscope) =willAextend horizontally in various directions while 'maintaining 'thelfixed "rightfangul'ar relation with respect'to each other. `iWth achange in 4heading of the aircraft, the 'absolute direction of the z-'zaxis fwill .not f'chang'e. "Therefore the 'gimbal ring I'Dwill stay iina `relatively fixed position while the frame assembly Zturns around withthe aircraft. This .relative motion ofthe frame and Hgimbal vring `will'cause displacement of the pointer `65 an :amount equivalent tothe'change in the aircraft 'heading, due to the action of bevel gears'6| -arid'fl lThe manner of operation of the reference dial 61 and itsrelative position with respect to the pointer 65 may be varied accordingto personal A:preference of the pilo'tbut the preferred manner ofusewillbe`des'cribed 'as follows. With the 'air- Ecraft 'proceeding on coursein normal level flight the 'gyroscope is caged 'manually and WhileAcaged -thelkrrobli isturned to position the pointer 65 in dahe uppermostposition. The gyro assembly G will now b'ein'ithe normal position withthe vaxis 'z--a .iin a horizontal attitude, and W'hen'the vgyros'copeiis "uncage'd Vby pulling out the knobth'e assemiblyfG=zaswell as theg'imbal ring Ill-will h'ol'd' the same position as obtained While thecaging 'mech-- .anism'was set. Nowtheknob 30 is again 'rotated t'ofsetthe card 61 in'positicn where/the dial read- Aing l'corresponds to theindicated heading obtained "the setfcourse. Anydeviationofthe'a'ircraft-from -thefstraigh't 'ahead course will 'be reflectedin a:'shi'ftof the pointer 65 in `one 'direction of rotation 'or the other,Vthus warning `Athe rpilot that :'he fhasFwandere-d oirhis rdesiredheading. A re- 'turnto the correct heading will of rcourse return lthep'ointer 'to the original position.

-"For illustration assume `that the aircraft .is heading north, as'indicatedby the Azero'settingof Fig. 2. Now assumingthatit isdesiredtto `head the :aircraft in a northeast direction, 'the pilot willoperatethe rudder to turn to the rrightat the :same time watching thepointer-65 Yasiiwturn's `"clockwise "When the pointer'reachesa'1point'4;5 fon the 'card 61 the pilot 'knows 'the turn is'comaplete'and he can keepothe pointer on this setting `fora'northeastheading. If he vis going `to"hold thisfcoursefor Isome distancehe 'may'cage the gyroscope and 'turn the 'pointer to th'e'uppermost -positionopposite one of the indices R ('seeiligs. f3 aand 3a.) .Then he willimmediately `Auncage the y'gyroscope'and again lturn the .knob "3D tobring thezfgraduation 4.5 on card`61 opposite .the pointer r'anduppermost index R. .Now '.fhekee'p's "the fpointer :in 'the straight upposition by fproper manipuiation offtheirudder he is assurefof beingcourse ina-ai northeast direction [ti is: noted ihowever "tha-tifthe-:construction .of Fig. ,3a yisused, athe pointer and lcard will turntogether in'th'e #caged position of the shaft 3| and gear lt-apthus`makingunnecessary the separate rotation of'ithe fcard'fl aftervuncaging the gyroscope as 'required with the construction of Fig. 3. Inmakingafturn :as `:explained above the aircraft will .be bankedduringthe turn, which will mean Ithat the spin axis z-zcwill stay'horizontal but the normally vertical 4axis y-y lWill take a positioncorrespond- -ing tothe angle of bank, oriroll. -As llong as'the y'bankydoes 1 not reach `an angle which 'allows fthe Vfcagingbar `|^5 `to'strike the stop I9, the normal V-relationfof the axes Will be restoredias the'air- `craft returns toa trim level position. .If `theigim` balring is .in position to place axis 'z-en'earfthe foro -and-aft .axis ofthe aircraft, the aXis'a-'z -may hold its :horizontal position withoutany apprec'iable .relative rotation ofthe gyro :assembly rGr relative tothe gimbal ring 1B (about the .Zrx viaxis). The Wholegyroscope assemblywill merely sturnzabout the e-.a axis, which axis isinowvlcoincildental'zwith 'the bank axis of the aircraft. Of course the'e-"e `axis is generally somewhere :between 'the position of -Fig. l andthe fore-and-aft lposition, so there 'is :usually fsome relativefmove-.fment of thegyro 'assembly Gand the gim'bal ring "l during a bankedturn. It might be'mention'ed rinpassing that'a bank or banked turn Which"does produce such relative .displacement ofthe assembly rG and thegimbal ring l0 Will connect -the torquerZB-'ZI--ZZ4 to the power supplythrough action of leveling switch IB-l'-IB, but Vtheair- `craft :is backin level 'flight so soonthat the torquer 'Will'not have time to effectany appreciable change -in the :relative position of the axes z-a andy-y. Formost turns and 'maneuvers the effect of the Ytor'quer may beignored, vits purpose as noted before being to maintain 'the rightangular rela- -tionof `axes'a-z and y-y during normal vlevel fl-ight.The reasons for maintaining the spin axis `.e-e horizontal in normalnight are beyond the fscope of the present description, but 'the reasonsare wellstated in The Theory of the Gyroscop'ic Compass by A. L.Rawlings v(second edition- .1944),fpages 16 to 23.

In 'understanding the operation of the gyro- 'scope k'with 'reference toits non-tumbling characteristics during violent maneuvers of the air-'craft,it must be emphasized that the axis z-z `will rarely if everextend directly vtransverse of the instrument and aircraft as shown inFig. l1, nor directly ina fore-and-aft direction either but mayapproximate these positions at times. It must 4:also 5be 1emphasizedthatthe roll and 'pitch maneuvers on modern fighter aircraft are oftenv veryextreme. For instance a normal .turnfor an aircraft flying at 500 milesper hour may result in a"90 bank angle. At times the aircraft may rollthrough 360 while on a more or lessstraight `course, and during'combatoperations almost any combinationof roll .and pitch maneuvers may beeffected bythepilot. On coming out of such maneuvers -it`is highlydesirable that the directional indicator vshow the 'relative directionof night, .justas `though the aircraft had been in level flight .during'the time of these maneuvers. The mannerin whichY the present instrumentaccomplishes this objective will now 'be 'set out.

Case I .-Roll maneuvers Considering the 'instrument in the position ofFig. al, Faroll of the'aircraft will cause the .frame aassembly 2 fand"the .gimbal 'ring 'l to `rotate around the relatively fixedgyroassembly G. If

the magnitude of the roll is less than the angleA separate again to oncemore assume the posi-- tion of Figs. 1 and 4. If the magnitude of theroll is equal to or greater than the angle A' or A, the end portion I5or I5V of the bar' I5y will engage the stop member'IS. The resultingreaction on the assembly G produces a pre-V the axis y-y however thev'precessing torqueV which develops upon contact of the stop members isreduced to a minimumand the conse'- quent turning action of the gimbalring at the larger bank angles is not so violent. The result is thatwhen the'stop members engage, the gimbal ring begins to turn ratherslowly and after a 90 swing from the position of Fig. 1 the torqueeifect disappears, although the ring'continues turning because of itsinertia. Furthermore with the gyro assembly G still in horizontal`position the leveling switch I6-I1-I8 is on, so that a very slighttorque is now applied to the ring IIJ by the torquer 20-2 I-22 whichacts to dampen or retard the turning motion of the ring. The result ofthe stop arrangement disclosed and the torquer action is to preventviolent turning action of the gimbal ring in rolls of large angle (say90 bank angle for example), and thus to prevent the gimbal ring fromrotating rapidly about the axis y-y in an uncontrolled fashion. If theroll is completed to a 90 position with the ring I9 turned about 180away from its original position the pilot usually comes back to levelflight. The stop action between members I5 and I9 now comes into playimmediately to cause a reverse torque on the gimbal ring I to return thering toward its original position, and allow the stop members toseparate as the gyro assembly G still holds to its original horizontalrelation. The effect of this simple 90 roll on the pointer 65 is tocause its swing through 180 as the gimbal ring rotates a like amount,and its return in the opposite direction of swing to the originalposition as the aircraft is maneuvered back into level night. It shouldbe mentioned that the bevel gears 6I and 62 are of the same size, sothat any angle of swing of the gimbal ring about the axis y-y will .beduplicated in the angle of swing of the indicator needle 65.

Assume now that the simple roll of about 90 as above described iscombined with a. turn of about 90 or less. The roll will probably beexecuted before any rudder is applied to prevent a possible skid of theaircraft. Thus as before the stop members I and I9 will contact and thering I0 will start to turn as though it was touched lightly by hand. Bythe time thek ring I0 has been displaced through an appreciable angle(say about 90), the turn of the aircraft will be Well started and thebanked turn will proceed. However on completion of the turn when theaircraft starts out of the steep bank, the stop members may not contactagain to swing the gimbal ring back as in the simple roll. Instead thecontact members will swing apart because the turn has caused the ring I0to take a new position more or less transverse to the fore-and-a'ft axisof the aircraft, instead of lined up therewith as shown in Fig. 1. Thepointer 65 will of course come to Vmined by the setting of the pointer65;

lo.. a stop so as to'showthe exact angle ofl turn com,-l pleted or the.new heading. Even if the-stop members do give the return motion to ringIl).y as in the case of a simple roll, the ring-will not: swingviolently or with an uncontrollable speed and in any case the gyroassembly Galways has time to come away from the stop engaging're` lationat the right time,'instead of being whirledl along with the mountingring and probably coming back to a stable position later with the *imstrument pointer showing an erroneous heading.

As a second example of the roll condition,'con sider the spin axis z-zextending along the fore-v and-aft axis of the aircraft. Now in a simpleroll of any magnitude `the whole gyroscope as'A sem-bly merely rotatesaround the rotor I4 andy no relative movement of the assembly G andring` I0 occurs. Of course if a turn is executedat ther same time theaxis z-z will leave this fore-and#- `aft position and then the roll willact on the in- Case II .-Pitch maneuvers Considering the instrument inthe position of Fig. 1, a pitch or loop of the aircraft will affect thegyroscope just the same as a roll where the axis 2 2 is ina'fore-and-aft direction; That is the gyroscope frame, mounting ring androtor case will merely rotate around the rapidly` turning rotor I4 andno relative displacement of' the gyro assembly G and mounting ring I0will occur. As noted in the precedingjparagraph however any turn at thesame time will cause'the 'axis of spin z--z to leave the transverserelation.

of Fig. 1, and then thering I0 may turn far enough away from therelatively stationary gyrov assembly G to cause engagement of the stop`members I5 and I9 with consequent turning action of the ring I0 aboutthe axis y-y, as explained above.v

In a pitch or loop maneuver Where the spin axis e-z is in a foreeand-aftposition or close thereto, the performance of the instrument is exactlysimilar to the case in which a roll is executed with the axis e-l-e inthe position of Figj 1. A pitch of suflicient magnitude to cause thestop member I9'to swing against the bar I5 will bring about a swing ofthe gimbal ring I0. Sincen this operation has been' stated above underCase I, it need not be repeated.

SUMMARY The non-tumbling characteristics of the presi 1 ent gyroscopicdirectional indicatorV are due largely to the specific relation of thestop mem` bers I5 and I9, which permits relatively large movements ofthev gyro "assembly G with respect to the gimbal ring I0 before anyengagement of the stop members. After the Stop members do engagetherotating action of the gimbal ring I0 about the axis y-y is notexcessivelyvr violent, thus allowing the gyro assembly G tol actindependently in its effort to hold to thef original xed position inspace. This position is determined by the action of the caging mechaf 4nism, although of course theorientationof the'jl spin axis e-z in thehorizontal plane is deter``.

The'V pointer may be held atl any reference point onf the dial bymaintaining a straight course of the" aircraft.' but for mostpurposes itis kpreferable '4 to placethe pointer in a straight lup positionfor anyextended flight. This makes a very convenient though arbitrary cruiseposition.

.. Because of the. proximity of the angles- A(v and.k

Ag," 'tp a. right` anglafr'reiation it might besup.-

posed that it would be preferable tdallow. aj full.-

.ar-zand y.-y.. Besides this also produces a sort,

of: dead-center relation of the gyro assembly G and the4 gimbal ring IU,requiring. some very definite force to move the gyro. assembly away fromthis.A so-called` gimbal lockedposition. Thusthe. previously statedvalues of anglesA and. A. are. considered to bathe, most desirable. Therange of these equal angles, as stated previously,.should be at'orsomewhere between, the values 82 and 8991. The. preferred value of thisangular relation is 866. It is further noted that the card 'l'isgraduated in degrees-from 0 to 361) like a. compass card.. However to,simplify the dial markings thenumerals thereonomit the lastzero, forinstance 18` indicates 180". Y

The embodiments of the. invention herein. shown and described are to. beregarded as. illustrative only and itis. to be understood that theinvention .is susceptible. to. variations, Amodifications. and changeswithin the scope of the appended' claims.

"We claim:

1.. A gyroscopic directional indicator. comprising, a normally verticalgimbal ring mounted,

means forv operatively connectingv said girnbal'v ring; and said pointerto Provide. for equi-angular rotation of said pointer andsaid gimbal.ring, a; rotatably mountedreference dial' directly be.- hind. saidpointer andconcentric withrespect thereto, a. cagingmechanism. operable.to` positively move said rto'rY case into .afposition whereinsaid rotorspin axis is at a right vangle to the axis of rotation of saidgimbalring, a slidable androtatable shaft for actuating.. saidy cagngmechanism by a sliding. movement4 thereof, means including an, elementfixed. on. saidshaft.

to 'rotate said pointer and said-'gimbal ringgwhen,

said. shaft is in the caged position andjupon ro.- tation of said shaft,andthe. latter means being operable to rotate said reference dial when.said shaftis in the uncaged positionand upon ro.- tation of said shaft.

2. A gyroscopic directional, indicatorv comprising, a normally verticalgimbal ring. mounted to rotate freely about a normally vertical axis, arotor case mounted to rotate within saidgimbal ring about aV normallyhorizontal axis. of rota,-v tion, a rotor capable of high speed;`rotation being rotatably mounted within said` rotor case on a normallyhorizontal spin axis lyingat. a right angle to the. axis ofv rotation.ofsaid rotor case. al rotatably mounted directionindicatingf pointer,means for operativelylconnecting said.A

k2 gixnnbal ring, and3A said. pointer to-provide for equi.- angularrotation of said pointerfand saidv g'imbal ring-J. a rotatablymounted.reference difal. di.-..

rectly behind saidpointer and concentric,v witli V respect thereto, a.caging mechanism; operable. to.

positively.: mov-e.- saidfrotor. case, into. a p osvtiorlI wherein saidrotor spin axis isat a rightl angle to the axis, of rotation.. of saidgimbalring,4 aA slidable and rotatable. shaft. for actuating, 'said`caging mechanism by. a. sliding movement thereof, meansineludinganelcmentl.. fixed; on..

case. mounted, to. rotate. within said gimbal ring.

abolita normally horizontal axis of rotation, a rotor. capable.. of highspeed rotation being ro.- tatably. mountedwithin said rotor caseon anormally horizontalfspin. axis lying at a right angle to the. axisofrotation of saidrotor case, a-ro.- tatably mounted direction.indicating pointer.

means for.. operatively connecting` said gnmbal..

ring and said pointer. to providefor. equi-angular rotation of saidpointerY andsaid. gimbal ring, a rotatably mounted reference dialdirectly behind said pointed concentric. with .respect thereto: andhaving gear. teeth, around the periphery thereof, a gearwheel having thesame diameter as said referencedial mountedy directly behind..

said .dial and being. rigidly. connected to said pointer rat the centerthereof, a caging mechanismoperable to positively move said roto-r caseVinto a. positionwhereinsaid, rotorV spin axis is at a right angle. to.the axis of rotation of said.

gimbalfringa slidabl'e,- and rotatable shaft for actuating saidcagingmechanism by an. inward.

slidingl movementthereof, pinion. means. on. said shaft engageable..with. said. reference dialand.V

said gear wheel simultaneously when said shaft isfinthe. cagedpositionthereof, and, said. pinion meansybyeing; engageable.. onlyvx/titlrrVsaid reference. dial when'saidshaftf is in the. uncaged po-l sitionthereof.

JOHN S. ADKINS. JOHNJ. HART.

REFERENCES CITED The following referentiesv aref off record in theirfile of-this patent:`

UNITEDLSTATES PATENTSv

